It is known in the art relating to supercharged engines to provide means for controlling the charging pressure supplied by the supercharger to the engine induction system, or charge supply system, in order to desirably control engine operating conditions. For example, in turbo-supercharged (turbocharged) engines, compressor outlet relief valves and exhaust turbine bypass (wastegate) valves are among devices which have been utilized to limit the engine charging pressure for various purposes. Commonly such valves are directly responsive to compressor discharge (boost) pressure to provide a maximum charge pressure limit within desirable engine operating capabilities. In addition, a wastegate valve can be actuated by an engine knock sensor to control maximum charge pressure as a function of the occurrence of knock. Knock control has also been accomplished in both supercharged and unsupercharged spark ignition engines by controlling engine ignition timing.
It has also been suggested in the prior art that engine performance can be optimized by maintaining constant a predetermined angular position of peak cylinder, or combustion chamber, pressure as it relates to a predetermined point in the cycle, such as the instant of minimum combustion chamber volume, or what is commonly known in piston engines as the top dead center position of the piston. For example, U.S. Pat. No. 4,063,538 Powell et al, granted Dec. 20, 1977, discusses optimization of engine performance through maintenance of a constant location of peak cylinder pressure utilizing automatic adjustment of engine spark timing to accomplish this purpose.
In each case, the various operating systems and controls are based upon the recognition of a significant functional relation between the engine parameter which is being controlled and the desired result of that control.